The present invention relates to an EMI/RFI shielding gasket. More particularly, the invention relates to a gasket having one or more areas covered by a conductive fiber flocking.
The operation of conventional electronic equipment is typically accompanied by the generation of radio frequency and/or electromagnetic radiation in the electronic circuitry of the electronic system. If not properly shielded, such radiation can cause considerable interference with unrelated equipment. Accordingly, it is necessary to effectively shield and ground all sources of radio frequency and electromagnetic radiation.
In instances where the radiation-generating equipment is permanently housed in a container, effective shielding may be accomplished easily through proper construction of the enclosure. However, when the equipment housing is provided with a readily openable access panel or door, effective radio frequency interference (RFI) or electromagnetic interference (EMI) shielding presents more of a problem. Many electronic installations such as computer rooms were made in the past without a full understanding of the effect of partially unshielded enclosures, such as access doors. Thus, manufacturers and users of older electronic equipment have attempted to upgrade the level of EMI/RFI shielding through retrofit installation of shielding gaskets around these access openings. Enclosures and equipment which are susceptible to electromagnetic/radiofrequency interference, e.g. aircraft, computer housings, and computer rooms, are now designed to include such shielding gaskets.
Conventional EMI/RFI shielding gaskets may comprise a conductive elastomer, a knitted wire mesh or a knitted wire mesh over an elastomeric core. These shielding gaskets may be attached to an enclosure by rivets, welds, or screws; by a continuous, roll-formed strip metal clip, to which a shielding gasket has been attached, or by a strip of pressure sensitive adhesive.
The shielding gasket is configured such that the gasket is brought into contact with a fixed surface of the enclosure when the door or panel is closed, effectively sealing off the narrow gap otherwise typically provided between a door or panel and the oppositely facing surface areas of the housing. Various configurations, often complex in shape, are designed in order to provide maximum shielding, while minimizing the closure force required. An example of such a low closure force gasket is shown in FIG. 1.
The electrical conductivity required for effective shielding has been provided in several ways. Elastomeric gaskets are rendered conductive by incorporating electrically conductive filler into the elastomer prior to formation of the gasket. Mesh gaskets are formed from metal mesh having high electrical conductivity, and are thus inherently conductive. Elastomer/mesh gaskets typically utilize both an elastomer and a highly conductive mesh.
Unfortunately, while these methods provide adequate shielding, they also significantly increase the cost and weight of the gasket as compared to a non-conductive gasket of similar size and shape. Applications involving mobile enclosures, particularly aerospace shielding applications, pose severe weight restrictions, and thus lightweight shielding gaskets are increasingly sought after.
Furthermore, the level of conductivity, and thus shielding, which can be obtained without exceeding practical limitations on weight and cost is limited. Thus it would be advantageous to provide a means of providing a highly conductive EMI/RFI shielding gasket which is low in cost and lightweight.
Another problem with conventional methods of rendering gaskets conductive arises when a gasket configuration similar to that shown in FIG. 1 is used. In order to provide the electrical continuity necessary for EMI/RFI shielding, it is only necessary that surfaces 3 and 4 of gasket 1 be conductive. (These surfaces 3 and 4 will be in continuous contact with the door and enclosure, respectively, thus forming a continuous electrical connection between the door and enclosure, while surface 2 will be compressed against itself, when the door or panel is closed.) In such applications, rendering the entire gasket conductive with conductive filler is wasteful and adds unnecessary weight, while conforming a metal mesh to the surface of the irregularly shaped gasket is often difficult and costly.
Thus it has been desired in the shielding field to provide a lightweight, low cost shielding gasket, and further to provide such a gasket which could be selectively rendered conductive over desired areas of its surface.